1. Field of the Invention
The invention relates generally to reproduction apparatus and more particularly to the production of both simplex and duplex copies by means of a single reproduction process in a copier.
2. Description of the Prior Art
Several techniques are known for forming duplex images on a final support medium such as a web or copy sheet. One such technique involves the use of two electrophotographic processes each of which includes an endless photoconductive drum or belt, and charge, expose, develop, transfer and cleaning stations disposed about the photoconductive drum or belt. The support medium is generally passed between the photoconductors and the first and second images formed respectively on said photoconductors are transferred to opposite sides of the support medium. This technique is disadvantageous in the cost of providing two complete photoconductive processes, and in the complexity, machine size and decreased reliability necessitated by the use of two such complete processes.
Another technique for forming duplex images involving one photoconductive system utilizes an intermediate image transfer member to receive the first image formed on the photoconductor before the image is transferred to the final support medium. The intermediate transfer member may be either a drum, roller or belt. The latter technique also suffers the disadvantages of increased cost, complexity and machine size and decreased reliability necessitated by the use of the intermediate transfer member. Additionally, the first image must go through two transfers increasing the probability of degradation in image quality on the final support medium.
A further technique for producing simplex or duplex copies utilizing only one electrophotographic process involves the formation of first images on the first sides of a plurality of copy sheets, the collection of all the copy sheets in an intermediate tray and then the transportation of the copies back through the electrophotographic process to form second images on the second sides of the copy sheets. This latter technique has several disadvantages. For example, since the first sides of all the copy sheets are developed before development of the second sides of the copy sheets a duplex copy is not available for proofreading until all of the first sides and one set of the second sides have been produced. Additionally, the relatively long paper paths required in passing copy sheets through the electrophotographic process twice increases the possibility of paper jams, reduces copier efficiency and productivity, and changes in environmental conditions between formation of the first and second images on the copy sheet may result in images of varying quality on opposite sides of a single sheet.
Still another duplex copying technique which is suitable for simplex copying involves a single electrophotographic process including forming first and second images sequentially on a photoconductor transferring the first image from the photoconductor to the first side of a copy sheet, fixing the first image to the copy sheet, inverting the copy sheet and, transferring the second image to the second side of the copy sheet. Such technique is disclosed in U.S. Pat. No. 3,506,347. This process has certain disadvantages in that the first image is fixed to the copy sheet before transfer of the second image thereto thus necessitating either the use of two fixing stations with attendant increased heat and power or the use of a solvent vapor tackifying station with problems of flamability and replenishment of the solvent.
An electrophotographic process for forming simplex images on copy sheets utilizing a pair of photoconductive members supported by an endless flexible belt is also disclosed in the prior art in U.S. Pat. No. 4,003,651.